ULSD corrosion issues may be caused by ethanol

15 September 2012

Battelle Memorial Institute has released the results of a study that investigated the phenomenon of accelerated corrosion observed in some underground storage tank (UST) systems storing and dispensing ultra low sulfur diesel fuel (ULSD). The study was funded by the American Petroleum Institute (API), the Petroleum Marketers Association Of America (PMAA) and other industry stakeholders.

The study was initiated two years ago after some UST operators reported accelerated corrosion occurrences primarily in submersible turbine pumps, drop tubes, sensor probes and dispenser components. The Battelle study sampled six sites nationwide that reported the accelerated corrosion phenomenon in ULSD systems.

The study concluded that corrosion occurring in systems storing and dispensing ULSD is likely due to the dispersal of acetic acid throughout USTs. The acetic acid is likely produced by bacteria feeding on low levels of ethanol contamination. Dispersed into the humid vapor space by disturbances during fuel deliveries, acetic acid is deposited throughout the UST system. This results in a cycle of wetting and drying of the equipment which concentrates the acetic acid on metallic equipment causing severe and rapid corrosion.

The source of the low level ethanol contamination present in sampled ULSD tanks is not yet known. Contamination may be occurring in pipelines, terminal systems, cargo tank compartments or manifold vent systems.

In their announcement, the PMAA emphasized that this phenomenon is still uncommon, it primarily affects system components rather than the tank itself and has not caused any known releases. It is too early to draw definitive conclusions on how ULSD tanks are being contaminated with ethanol or why accelerated corrosion occurs in a very small percentage of ULSD tanks while the majority of ULSD tanks remain largely unaffected.

The stakeholders who sponsored the study are currently deciding whether to move forward with further research. Battelle recommends that additional research be focused on samples from a larger and more diverse set of USTs over a longer period of time. The study would sample and monitor ULSD tank systems with and without accelerated corrosion events and investigate the possible source of ethanol contamination.

The conclusions of the study have been questioned by the Renewable Fuels Association. “Battelle’s report attempts to draw meaningful conclusions from surprisingly few data points which leave fuel experts with many questions”, said RFA in a blog post.